Contained growing space and environmental control system

ABSTRACT

A controlled and closed agricultural system includes a growing space and an air handling system having a heat exchanger and cooling coil. The heat exchanger is capable of transferring sensible and latent heat and is in fluid connection with a recirculating air duct and an outside air duct. The recirculating air duct is in fluid connection with the growing space and one or more recirculation fans, while the outside air duct is in fluid connection with one or more outside air fans positioned to cause outside air to flow countercurrent to recirculating air through the heat exchanger. A cooling coil is positioned within the recirculating air duct, downstream of and in series with the heat exchanger. The cooling coil circulates a heat transfer fluid to remove additional heat from the recirculating air.

INCORPORATION BY REFERENCE STATEMENT

This application claims priority to U.S. application Ser. No. 14/878,066filed on Oct. 8, 2015, the content of which is hereby expresslyincorporated herein by reference in its entirety.

BACKGROUND 1. Field of the Presently Disclosed and/or Claimed InventiveConcepts

The inventive concepts disclosed and claimed herein relate generally tosystems and methods for controlling the interior environment of anenclosure, and more particularly, but not by way of limitation, tosystems and methods for controlling the temperature, humidity, andoptionally CO₂ levels in a contained space.

2. Brief Description of Related Art

Greenhouses require temperature and humidity control to maintain dryfoliage and plant health. Lighting can cause excessive heat and highhumidity, especially free water on the plant foliage, promotes thedevelopment of foliar diseases, such as tomato blight, gray mold, andmildews in various crops. Such diseases substantially reduce crop yield,impair product quality, and require pesticides for control.

Replacing the greenhouse air with external air is a customary method fordecreasing the humidity in a greenhouse. External cold air, with lowabsolute humidity, replaces the warmer greenhouse air and absorbs theexcess water that evaporates. However, such methods are energyinefficient and can bring unwanted contaminants into the growing space.

It would therefore be desirable to have a controlled and containedgrowing space with recirculation of most or all of the air. It wouldalso be desirable to have a system to control the temperature, humidity,and optionally the CO₂ levels in the contained growing space that doesnot require addition of outside air. This disclosure proposes a methodand system that accomplishes this.

BRIEF SUMMARY

The inventive concepts disclosed and claimed herein relate generally tosystems and methods for controlling the environment, including lighting,temperature, humidity, and optionally CO₂ levels in an interior of anenclosure in which plants are grown. In one embodiment, a controlled andclosed agricultural system includes a growing space and an air handlingsystem having a heat exchanger and a cooling coil. The heat exchanger iscapable of transferring sensible and latent heat and is fluid connectionwith a recirculating air duct and an outside air duct. The recirculatingair duct is isolated from the outside air duct and is in fluidconnection with the growing space and one or more recirculation fans,while the outside air duct is in fluid connection with one or moreoutside air fans positioned to cause outside air to flow in apredetermined manner, e.g., countercurrent to the recirculating airthough the heat exchanger. A cooling coil is positioned within therecirculating air duct, downstream of and in series with the heatexchanger. The cooling coil circulates a heat transfer fluid to removeheat from the recirculating air.

In another embodiment, a controlled and closed agricultural systemincludes a growing space and an air handling system having a first heatexchanger, a second heat exchanger, and a cooling coil. The first heatexchanger is capable of transferring sensible heat and is in fluidconnection with a recirculating air duct and an adjacent outside airduct. The second heat exchanger is capable of transferring latent heatand is positioned in series with the first heat exchanger and is influid connection with the recirculating air duct and the outside airduct. The recirculating air duct is isolated from the outside air ductand is in fluid connection with the growing space and one or morerecirculation fans. The outside air duct is in fluid connection with oneor more outside air fans positioned to cause outside air to flow in apredetermined manner, e.g., countercurrent to the recirculating air. Acooling coil is positioned within the recirculating air duct, downstreamof and in series with the first heat exchanger. The cooling coilcirculates a heat transfer fluid to remove heat from the recirculatingair.

In yet another embodiment, a method for treating air within a growingspace of a closed agricultural system includes the following steps. Airis recirculated from a contained growing space through an air handlingsystem having at least one heat exchanger to reduce the energy contentof the recirculating air. The recirculating air exiting the heatexchanger(s) is passed across a cooling coil circulating a heat transferfluid to further reduce the heat content of the recirculating air. Therecirculating air passing the cooling coil is returned to the containedgrowing space of the closed agricultural system. Outside air is passedthrough the heat exchanger (s) counter-current to and separated from therecirculating air.

BRIEF DESCRIPTION OF THE DRAWINGS

Like reference numerals in the figures represent and refer to the sameor similar element or function. Implementations of the disclosure may bebetter understood when consideration is given to the following detaileddescription thereof. Such description makes reference to the annexedpictorial illustrations, schematics, graphs, and drawings. The figuresare not necessarily to scale and certain features and certain views ofthe figures may be shown exaggerated, to scale or in schematic in theinterest of clarity and conciseness. All of the drawings are for thepurpose of describing selected versions of the present invention and arenot intended to limit the scope of the present invention. In thedrawings:

FIG. 1 illustrates an exemplary system for treating air within a closedstructure for growing plants in accordance with the present disclosure.

FIG. 2 is an elevation view of an exemplary closed growing space and airhandling system in accordance with the present disclosure.

FIG. 3 is a plan view of an upper deck of the air handling system ofFIG. 2.

FIG. 4 is a plan view of a middle deck of the air handling system ofFIG. 2.

FIG. 5 is a plan view of a lower deck of the air handling system of FIG.2.

FIG. 6 is a plan view of the air handling system described in Example 1.

FIG. 7 is a flow diagram for the air handling system described inExample 2.

FIG. 8 is a flow diagram for the air handling system described inExample 3.

FIG. 9 is a flow diagram for the air handling system described inExample 4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the inventive conceptsdisclosed herein in detail, it is to be understood that the inventiveconcepts are not limited in their application to the details ofconstruction, exemplary data, and/or the arrangement of the componentsset forth in the following description, or illustrated in the drawings.The presently disclosed and claimed inventive concepts are capable ofother embodiments or of being practiced or carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein is for purpose of description only and should not beregarded as limiting in any way.

In the following detailed description of embodiments of the inventiveconcepts, numerous specific details are set forth in order to provide amore thorough understanding of the inventive concepts. However, it willbe apparent to one of ordinary skill in the art that the inventiveconcepts within the disclosure may be practiced without these specificdetails. In other instances, well-known features have not been describedin detail to avoid unnecessarily complicating the instant disclosure.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discreet components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited as well as any other order that is logically possible.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. For example, a condition A or Bis satisfied by anyone of the following: A is true (or present) and B isfalse (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the inventive concept. Thisdescription should be read to include one or more and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Use of the term “plurality” is meant to convey “more than one” unlessexpressly stated to the contrary.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

Reference to an energy wheel herein and in the appending claims refersto a type of rotating air-to-air heat exchanger. An energy wheel thattransfers only sensible heat is referred to herein and in the appendingclaims as a “heat wheel.” An energy wheel that transfers only latentheat is referred to herein and in the appending claims as a “desiccantwheel.” An energy wheel that can transfer both sensible heat and latentheat is referred to herein and in the appending claims as an “enthalpywheel.”

References to agricultural growing spaces are for example only, and theinventive concepts disclosed herein can be used with any closed,contained or nearly-closed and contained space.

Agricultural growing spaces generate high humidity due to planttranspiration and high sensible heat loads due to either sunlight orgrow lights. To maintain a growing space with low levels ofcontamination, it is desirable to remove the excess heat and moisturewithout adding outside air to the contained growing space.

Referring now to FIG. 1 and FIG. 2, a controlled agricultural system 10includes a growing space 12, and an air handling system 13. The airhandling system 13 includes an enthalpy wheel 14, a cooling coil 16 andoptionally a condensing coil 18. The enthalpy wheel 14 is capable oftransferring sensible and latent heat and is positioned in and rotatablethrough a recirculating air duct 22 and an outside air duct 24 adjacentthe recirculating air duct 22. The recirculating air duct 22 is in fluidconnection with the growing space 12 and one or more recirculating airfans 26, while the outside air duct 24 is in fluid connection with oneor more outside air fans 28 positioned to cause outside air to flowcountercurrent to recirculating air. The cooling coil 16 is positionedwithin the recirculating air duct 22, downstream of and in series withthe enthalpy wheel 14. The cooling coil 16 circulates a heat transferfluid through a heat transfer fluid line 30 to remove heat from therecirculating air.

The controlled agricultural system 10 can be operated to control theenvironment within the growing space 12 defined by side walls 34 and anoverhead wall 36. The side walls 34 and overhead wall 36 can be made ofglass as traditional greenhouses, with louvers or the like to controlthe amount of sunlight entering the growing space 12. In one embodiment,the side walls 34 and overhead wall 36 are opaque to sunlight, andartificial light is provided to plants growing in the growing space 12by grow lights 38. The use of grow lights 38 provides additionalflexibility and energy savings in that the environmental factors can becontrolled and therefore optimized in terms of plant yield and energyefficiency.

For example, in some climates it may be advantageous to have artificiallight at night when the temperature of the growing space exterior iscooler, and darkness during the day when the temperature of the growingspace exterior is much hotter, thereby lessening the heat load that mustbe removed from the recirculating air. Further, the use of grow lights38 allows the duration of light and darkness to be optimized for bothplant yield and energy costs.

In one embodiment, actual sunlight is completely replaced by artificiallight. In another embodiment, the light wavelengths, light intensity,and light duration can be completely artificial and controlled, therebyeliminating inefficiencies associated with weather and seasonalconditions.

The growing space 12 can be conditioned year round and outside air canbe avoided thereby eliminating problems due to variable seasons, pests,air contaminants such as molds, pollen, etc. The constant cooling of theair within the growing space 12 can result in significant savings inenergy use and resulting costs.

In one embodiment, the air in the growing space 12 is circulated suchthat it is not mixed with outside air, thereby minimizing contaminationof the growing space 12. Recirculating air fans 26 draw air from thegrowing space 12 through the air handling system 13, separated from andin counter current flow to the outside air which is pulled from outsidethe air handling system 13 by the outside air fans 28 and may becontrolled, at least in part, by an outside air damper 39.

In one embodiment, the enthalpy wheel 14 is positioned in and rotatablethrough a bifurcated duct 20. A separating wall 40 bifurcates at least aportion of the duct 20, such that the separating wall 40 separates arecirculating air portion 22′ from an outside air portion 24′. Therecirculating air portion 22′ of the bifurcated duct 20 is sometimesreferred to as the recirculating air duct 22. Likewise, the outside airportion 24′ of the bifurcated duct 20 is sometimes referred to herein asthe outside air duct 24.

The enthalpy wheel 14 can be positioned within the bifurcated duct 20,or within the recirculating air duct 22 and the outside air duct 24,such that warm moist air recirculated from the growing space 12 passesthough one portion of the enthalpy wheel 14 and outside air passes inthe opposite direction through the remaining portion of the enthalpywheel 14. Brush seals and the like may be used to maintain isolationbetween the recirculating air and the outside air or at least minimizecontamination of the recirculating air with outside air.

Energy wheels are a type of air-to-air heat exchanger that can not onlytransfer sensible heat but also latent heat. When both temperature andmoisture are transferred, the energy wheel is considered an enthalpywheel. The rotating energy wheel heat exchanger is composed of arotating cylinder filled with an air permeable material resulting in alarge surface area for the sensible energy transfer. As the wheelrotates between the recirculating air portion 22′ and the outside airportion 24′ of the bifurcated duct 20, or through the recirculating airduct 22 adjacent the outside air duct 24, the wheel picks up sensibleenergy (heat) and releases the sensible energy into a relatively colderoutside air stream. The driving force behind the exchange is thedifference in temperatures between the opposing air streams which isalso called the thermal gradient. Nonlimiting examples of suitablematerial used includes polymer, aluminum, and synthetic fiber.

The moisture or latent energy exchange in enthalpy wheels isaccomplished through the use of desiccants. Desiccants transfer moisturethrough the process of adsorption which is predominately driven by thedifference in the partial pressure of vapor within the opposing airstreams. Nonlimiting examples of suitable desiccants include silica geland molecular sieves.

In some environments, modulating dampers can be used to control theflowrate of outside air. Modulating the wheel speed, preheating the air,and stop/jogging the system offer additional means to control the energytransfer. Cross-contamination of the contaminants via the desiccant canalso be a concern but can be avoided for example through the use of aselective desiccant like a molecular sieve.

In one embodiment, a mixing damper 42 is positioned in the outside airduct 24, or the outside air portion 24′ of the bifurcated duct 20,downstream of the enthalpy wheel 14, and can be used to control theamount of outside air. For example, one or more industry standardmodulating damper(s) can be positioned in parallel with the enthalpywheel 14 and modulated in concert with the outside air damper 39 tomaintain a desired operation and performance of the enthalpy wheel 14.

Temperature and relative humidity measurements can be taken using, forexample, industry standard temperature and humidity sensors. Temperatureand relative humidity measurements of the outside air stream enteringthe enthalpy wheel 14, the recirculating air entering the enthalpy wheel14, and the recirculating air exiting the enthalpy wheel 14 can be usedto control the speed of the outside air fans 28, the speed of theenthalpy wheel, and control operation of the direct expansion evaporatorcooling coil 16.

The cooling coil 16 can further cool the recirculating air exiting theenthalpy wheel 14. The cooling coil 16 can circulate chilled water, amixture of chilled water and glycol, refrigerant, and the like.

In one embodiment, chilled water is produced in another portion of thefacility housing the controlled agricultural system and is utilized tofurther cool recirculating air exiting the enthalpy wheel 14.

In one embodiment, the cooling coil 16 is a direct expansion evaporatorcooling coil. A compressor 32 and condensing coil 18 are external to therecirculating air duct 22, or the recirculating air portion 22′ of thebifurcated duct 20, and use outside air to remove heat from the heattransfer fluid.

Design and operation of evaporator cooling coils are well understood bythose skilled in the art. Typically condensed and pressurized liquidrefrigerant is routed through an expansion valve where it undergoes anabrupt reduction in pressure. That pressure reduction results in flashevaporation of a part of the liquid refrigerant, thereby lowering itstemperature. The cold refrigerant is then routed through the evaporatorcooling coil. Air fans blow the recirculating air across the evaporator,causing the liquid part of the cold refrigerant mixture to evaporate aswell, further lowering the temperature. The recirculating air istherefore cooled by heat transfer from the direct expansion evaporatorcooling coil 16.

Circulating refrigerant vapor enters the compressor 32 and is compressedto a higher pressure, resulting in a higher temperature as well. Thehot, compressed refrigerant vapor is at a temperature and pressure atwhich it can be condensed and is routed through the condensing coil 18located in the outside air duct 24, or the outside air portion 24′ ofthe bifurcated duct 20. Outside air fan(s) 28 causes outside air exitingthe enthalpy wheel 14 to flow across the condensing coil 18. The cooleroutside air flowing across the condensing coil 18 causes the refrigerantin the coil to condense into a liquid. Thus, in summary, the circulatingrefrigerant removes heat from the recirculating air and the heat iscarried away by the outside air.

In one embodiment, for example when weather or other circumstances causethe recirculating air to be colder than desired, the refrigeration cyclecan be reversed and refrigerant is pumped in the opposite direction. Theoverall effect is the opposite, and the recirculating air is heatedinstead of cooled.

In one embodiment, for example when the recirculating air becomes coolerthan desired for recirculating to the growing space 12, one or moreheaters 44 in the recirculating air duct 22, or the recirculating airportion 22′ of the bifurcated duct 20, can be utilized to control thetemperature of the recirculating air and the growing space 12.Non-limiting examples of suitable heaters include electrical resistanceheaters, hot water radiators, natural gas furnaces, and the like.

A CO₂ generator 46 can be used to add CO₂ to the recirculating air duct22, or the recirculating air portion 22′ of the bifurcated duct 20. Anassociated CO₂ sensor 48 can sense and read the CO₂ level in therecirculating air and input the level to a CO₂ controller 50. The CO₂generator 46 is controlled by the CO₂ controller 50 to maintain the CO₂content at a set point or set range.

In one embodiment, the CO₂ generator 46 comprises a natural gas burnerlocated in the outside air duct 24, or the outside air portion 24′ ofthe bifurcated duct 20. Locating the natural gas burner in the outsideair portion allows a majority of the heat related to combustion toexhaust directly outside. Flue gas from the natural gas burner isdelivered in controlled amounts to the recirculating air. A flue gas fan52 located in the separating wall 40 can be utilized, for example tometer the flue gas to the recirculating air portion 22′ of thebifurcated duct 20 and thereby maintain the CO₂ content at a set pointor set range.

In one embodiment, a control louver 54 is also used to purge excess CO₂from the recirculating air duct 22, or the recirculating air portion 22′of the bifurcated duct 20, to maintain the CO₂ content at a set point orset range.

In one embodiment, an industry standard CO₂ sensor 48 is installed inthe recirculating air duct 22, or in the recirculating air portion 22′of the bifurcated duct 20. The CO₂ sensor 48 feeds back to the CO₂controller 50 within a central control system 55 to determine if thenatural gas burner should fire and at what rate the CO₂-containing fluegas should be metered into the air handling system 13 to meet ormaintain a user-defined CO₂ set point.

In one embodiment, the air handling system 13 includes a separatedesiccant wheel 56 for removing moisture from the recirculating air. Thedesiccant wheel 56 is positioned in and rotatable through both therecirculating air duct 22 and the outside air duct 24 such that warmmoist air recirculated from the growing space 12 passes though oneportion of the desiccant wheel 56 and heated outside air exiting thecondensing coil 18 passes in the opposite direction through theremaining portion of the desiccant wheel 56. A separate heat wheel 57capable of transferring sensible heat also positioned in and rotatablethrough both the recirculating air duct and the outside air duct. Theheat wheel 57 cools dried recirculating air exiting the desiccant wheel56 and transfers the sensible heat to outside air upstream of thedesiccant wheel 56.

As described above for the enthalpy wheel 14, the desiccant wheel 56 iscomposed of a rotating cylinder filled with an air permeable materialcomprising desiccant. As the desiccant wheel 56 rotates between therecirculating air duct 22 and the outside air duct 24, it picks upmoisture from the moist recirculating air and releases it into the drieroutside air stream. Desiccants transfer moisture through the process ofadsorption which is predominately driven by the difference in thepartial pressure of vapor within the opposing air streams. Suitabledesiccants include silica gel, and molecular sieves. The outside airwith absorbed heat and humidity is then discharged from the air handlingsystem 13 and returned to the atmosphere.

In one embodiment, a recirculating air filter 58 positioned in therecirculating air duct 22 removes particulate from the recirculating airbefore feeding it back to the growing space 12. Design and operation ofair filters are well understood by those skilled in the art.

An outside air filter 60 can be positioned in the outside air duct 24 toremove particulate from the outside air prior to passing it through theenthalpy wheel 14 or the desiccant wheel 56 and heat wheel 57. Removalof particulate can aid in reducing the maintenance of the wheels.

The central control system 55 can modulate the fans, wheel(s), andoptionally the compressor to minimize energy consumption. Components ofthe system described above can be variable speed. The fans can vary thevolume of air moved and the wheel speed(s) can vary to maximizeefficiency. The mechanical cooling system including the cooling coil 16optimally provides only the cooling necessary. Control logic for thecomponents can be housed in a common control cabinet.

In the embodiment shown in FIG. 2, the air handling system 13 isconstructed adjacent to the growing space 12 with a recirculating airoutlet 62 originating from a far side of the growing space 12, and arecirculating air intake 64 proximate the air handling system 13. Whilenumerous layouts can be used, separation of the recirculating air outletand intake 62 and 64, respectively, improves efficiency of airreplacement in the growing space 12. FIG. 3 through FIG. 5 show possibleequipment layouts in three levels of the air handling system 13.

A method for treating air within a growing space of a closedagricultural system includes temperature and moisture control equipmentas described above. Recirculating air from a contained growing space ispassed through an air handling system comprising at least one energywheel to reduce the energy content of the recirculating air. Therecirculating air exiting the energy wheel(s) is passed across a coolingcoil circulating a heat transfer fluid to further reduce the heatcontent of the recirculating air. The recirculating air passing thecooling coil is then returned to the contained growing space. Outsideair is passed through the energy wheel(s) counter-current to andseparated from the recirculating air.

In one embodiment, the recirculating air exiting the energy wheel(s) canbe passed across a direct expansion evaporator cooling coil circulatinga heat transfer fluid to further reduce the heat content of therecirculating air before returning the air to the main portion of theclosed structure. The heat transfer fluid is cooled by circulatingthrough a compressor and a condensing coil in contact with the outsideair.

In one embodiment the energy wheel comprises an enthalpy wheel to reducethe temperature and the moisture content of the recirculating air. Inanother embodiment, the energy wheels comprise both a desiccant wheel toreduce the moisture content of the recirculating air and a heat wheel toreduce the temperature of the recirculating air.

The method for treating air within a growing space of a closedagricultural system can additionally include monitoring the CO₂ contentof air circulated from the growing space. CO₂ is added if the CO₂content is below a desired value, and a portion of the recirculating airis vented if the CO₂ content is above a level determined to be harmful.

In the following examples, specific controlled and closed agriculturalsystems are described. However, the present inventive concept(s) is notto be limited in its application to the specific equipment, plantlayout, and operating methods. Rather, the Examples are simply providedas one of various embodiments and are meant to be exemplary, notexhaustive.

Example 1

In some applications, the humidity level in the closed agriculturalsystem requires more extensive dehumidification than normal. As shown inFIG. 6, a second desiccant wheel is installed downstream of therecirculation fans and condensing coil. The enthalpy wheel is replacedwith a heat wheel (sensible heat-only wheel, no desiccant). A condensingcoil or a natural gas burner acts as regeneration heat for the latentheat-only wheel. As the desiccant wheel rotates from one air stream tothe other it adsorbs the moisture from the recirculation air. Thatmoisture is then released to the outside air stream. To aid in thatrelease, regeneration heat (condensing coil heat and/or optional naturalgas burner) is applied to the air entering the wheel in the outside airstream. An additional set of temperature and relative humidity sensorsare installed downstream of the desiccant wheel. The control systemvaries the speed of the desiccant wheel to meet the user definedrelative humidity set point. Similarly, the control system varies theheat wheel to meet the user defined temperature set point.

Example 2

The efficiency of the air handling system depends on the outside airtemperature and humidity. When conditions are favorable (cooler dryerweather), the system is capable of transferring the heat and humidity ofthe recirculation air through the enthalpy wheel to the cooler and dryeroutside air. As indicated in the flow diagram shown in FIG. 7, 57° F.outside air with 40.7 grains of moisture is coming into the unit andinto the enthalpy wheel. The resulting recirculation air temperature andgrain level off the wheel (60° F./45.1 grains) to provide 100% of therequired heating and dehumidification.

Example 3

As the outside air temperature and humidity go up, the enthalpy wheelcan still provide value by “pre-conditioning” the recirculation airbefore the cooling coil. In the flow diagram shown in FIG. 8, 57° F.outside air with 60.6 grains is entering the air handling unit and theenthalpy wheel. The resulting recirculation air temperature and grainlevel off the wheel (60° F./63.2 Grains) is sufficient to cool therecirculating air, but it is not sufficient to remove the moisture fromthe recirculating air. As a result the air handling unit control systemshall enable the mechanical cooling to remove the additional grains ofmoisture from the recirculation air, down to the user defined set pointof 48 grains. In order to remove the moisture the cooling coil must overcool the air, 50° F. The over cooled air could potentially over cool therecirculating air, therefore the air handling unit control system shallenable the heat source to heat the recirculating air to the user definedset point.

Example 4

At some point the outside air will be too hot and too wet for the airhandling system to be able to transfer heat and humidity form therecirculating air stream to the outside air stream. In the flow diagramshown in FIG. 9, when the control system determines that there is nobenefit from the enthalpy wheel, the wheel shall stop. At this point theair handling unit is capable of mechanically cooling all therecirculating air to meet the user defined set point.

From the above description, it is clear that the inventive concept(s)disclosed herein is well adapted to carry out the objects and to attainthe advantages mentioned herein as well as those inherent in theinventive concept disclosed herein. While exemplary embodiments of theinventive concept disclosed herein have been described for purposes ofthis disclosure, it will be understood that numerous changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are accomplished without departing from the scope of the inventiveconcept disclosed herein and defined by the appended claims.

What is claimed is:
 1. A controlled agricultural system, comprising: agrowing space; and a heat exchanger capable of transferring sensible andlatent heat, the heat exchanger in fluid connection with both arecirculating air duct and an outside air duct, the recirculating airduct in fluid connection with the growing space and one or morerecirculation fans, the outside air duct in fluid connection with one ormore outside air fans positioned to cause outside air to flowcountercurrent to recirculating air through the heat exchanger; and acooling coil within the recirculating air duct, downstream of and inseries with the heat exchanger, the cooling coil circulating a heattransfer fluid to remove heat from the recirculating air.
 2. Thecontrolled agricultural system of claim 1, wherein the growing spacecomprises a closed green house.
 3. The controlled agricultural system ofclaim 1, wherein the growing space is closed and comprises lightimpermeable outer walls and grow lights positioned inside the closedgrowing space.
 4. The controlled agricultural system of claim 1, whereinthe cooling coil comprises a direct expansion evaporation cooling coil.5. The controlled agricultural system of claim 4, further comprising acompressor and a condensing coil external to the recirculating air ductfor removing heat from the heat transfer fluid.
 6. The controlledagricultural system of claim 1, further comprising a recirculationdamper within the outside air duct and positioned to recirculate aportion of the outside air from downstream of the heat exchanger toupstream of the heat exchanger.
 7. The controlled agricultural system ofclaim 1, further comprising a heat source positioned to provide heat tothe recirculating air downstream of the heat exchanger.
 8. Thecontrolled agricultural system of claim 1, further comprising a CO₂monitor positioned to monitor a CO₂ content in the recirculating airduct.
 9. The controlled agricultural system of claim 8, furthercomprising a CO₂ generator and CO₂ controller in communication with theCO₂ monitor, the CO₂ generator having an outlet positioned to add CO₂ tothe recirculating air duct.
 10. A controlled agricultural system,comprising: a growing space; and a first heat exchanger capable oftransferring sensible heat, the first heat exchanger in fluid connectionwith both a recirculating air duct and an outside air duct, therecirculating air duct in fluid connection with the growing space andone or more recirculation fans, the outside air duct in fluid connectionwith one or more outside air fans positioned to cause outside air toflow countercurrent to recirculating air; and; a second heat exchangercapable of transferring latent heat, the second heat exchanger in fluidconnection with the recirculating air duct in series with the heat wheelsuch that recirculating air passes through the second heat exchangerprior to passing through the first heat exchanger; and a cooling coilwithin the recirculating air duct, downstream of and in series with thefirst heat exchanger, the cooling coil circulating a heat transfer fluidto remove heat from the recirculating air.
 11. The controlledagricultural system of claim 10, wherein the growing space comprises aclosed green house.
 12. The controlled agricultural system of claim 10,wherein the growing space is closed and comprises light impermeableouter walls and grow lights positioned inside the closed growing space.13. The controlled and closed agricultural system of claim 10, furthercomprising a compressor and a condensing coil external to therecirculating air duct for removing heat from the heat transfer fluid,and wherein the cooling coil comprises a direct expansion evaporationcooling coil.
 14. A method for treating air within a growing space of aclosed agricultural system, the method comprising: recirculating airfrom a contained growing space through an air handling system, the airhandling system comprising at least one heat exchanger to reduce theenergy content of the recirculating air; passing the recirculating airexiting the at least one heat exchanger across a cooling coilcirculating a heat transfer fluid to further reduce the heat content ofthe recirculating air; returning the recirculating air passing thecooling coil to the contained growing space; and passing outside airthrough the at least one additional heat exchanger, the outside airpassing counter-current to and separated from the recirculating air. 15.The method of claim 14, further comprising circulating the heat transferfluid through a compressor and a condensing coil while passing outsideair across the condensing coil to cool and condense the heat transferfluid, and wherein the cooling coil comprises a direct expansionevaporator cooling coil.
 16. The method of claim 14, wherein the atleast one heat exchanger comprises an enthalpy wheel.
 17. The method ofclaim 14, wherein the at least one heat exchanger comprises a desiccantwheel and a heat wheel.
 18. The method of claim 14, further comprisingmonitoring a temperature and humidity of the recirculating air.
 19. Themethod of claim 14, further comprising controlling the temperature andhumidity of the growing space by monitoring the temperature and humidityof the recirculating air in the recirculating air duct downstream of thecooling coil and controlling operation of the at least one heatexchanger and the cooling coil.
 20. A controlled air system, comprising:a contained space; a heat exchanger capable of transferring sensible andlatent heat, the heat exchanger in fluid connection with a bifurcatedduct, the duct having a recirculating air portion and an outside airportion, the recirculating air portion in fluid connection with thecontained space and one or more recirculation fans, the outside airportion in fluid connection with one or more outside air fans positionedto cause outside air to flow countercurrent to recirculating air; and acooling coil within the recirculating air portion of the bifurcatedduct, downstream of and in series with the heat exchanger, the coolingcoil circulating a heat transfer fluid to remove heat from therecirculating air.